The present invention relates to density detection using discrete photon counting, and more particularly to using discrete photon counting to generate an image indicative of the densities in a target object. Even more particularly, the present invention relates to using discrete photon counting to perform density measurements in a target object and generating an image of the contents of such target object in response thereto.
There are many instances in the security or customs field when it is necessary to examine or inspect, in a non-destructive way, the contents of a target object, such as a closed package, box, suitcase, cargo container, automobile semi-trailer, tanker truck, railroad car, e.g., box car or tanker car, or the like. For example, customs departments are routinely charged with the responsibility of inspecting vehicles coming into a country to make sure such packages do not contain drugs or other contraband. Similarly, drug smugglers frequently carry out their criminal acts by hiding illegal drugs in vehicles such tanker trucks, and then sending the trucks through a border checkpoint. When security personnel encounter suspicious vehicles or other containers being transported over international boundaries, they must perform a careful inspection of such vehicles to ascertain their contents.
When suspicious vehicles are discovered, they generally must be examined or inspected on location in what is referred to as a "secondary inspection area." If secondary inspection reveals the presence of contraband (e.g., drugs), then the vehicle may be impounded, the driver arrested, and the contraband disposed of. If, on the other hand, the examination reveals the absence of contraband, then the vehicle may be allowed to proceed in a normal manner.
The process used to examine or inspect a suspicious vehicle should be quick, simple, and as unintrusive as possible. Unfortunately, conventional inspection mechanisms require either visual inspection by others and/or scent inspection by dogs. These conventional methods require that the vehicle stop and wait for the inspection to be completed, which can take a half hour or more. This is both inconvenient and time consuming for both customs officials and the vehicle drivers and occupants. Furthermore, such inspection may put officers at personal risk if a vehicle has been booby trapped or if the vehicle's driver or other occupants become nervous and decide to attack the customs officer inspecting their vehicle. What is needed, therefore, is a non-invasive technique for inspecting the contents of a suspicious vehicle without requiring that the vehicle be stopped and manually inspected.
One attempt to satisfy this need involves the use of high levels of radiation to determine the densities of the vehicle and/or the contents of such vehicle. Unfortunately, this approach requires that the vehicle be stopped and evacuated prior to inspection, because such high levels of radiation can be physically harmful to the vehicle's occupants if they remain in the vehicle during inspection. Disadvantageously, inspection using high levels of radiation not only requires that the vehicle be stopped, and therefore delayed, but poses a risk to stowaways that may be aboard the vehicle, and unwilling to voluntarily evacuate, when the vehicle is stopped for inspection. Therefore, what is needed is a non-invasive technique for inspecting the contents of a suspicious vehicle without requiring the use of high levels of radiation.
A further problem posed by manual inspection techniques arises when tanker trucks or railroad cars, after having been emptied, seek to cross a border in order to refill. Because such tankers cannot be completely emptied without releasing the pressure in such tankers and venting noxious gasses into the atmosphere, the tankers typically are kept nominally under pressure. (The venting of noxious gases would be hazardous and ecologically unacceptable.) Thus, the contents of such tankers typically go uninspected by customs agents in order to avoid the venting of such gases. Unfortunately, drugs smugglers are well aware of this fact, and therefore utilize tanker trucks and railroad cars to import illegal drugs, knowing that they will not be inspected at the border. This provides just one of numerous additional examples of cases where invasive or intrusive inspection into vehicles, or other containers, is not feasible or desirable. Thus, further emphasizing the need for a non-intrusive approach to vehicle inspection.
The present invention advantageously addresses the above and other needs.